The invention concerns an apparatus for early detection of a tachycardia of a heart.
The human heart, can go into physiologically disturbing and possibly fatal states. One such state is a tachycardia, which is distinguished by very rapidly succeeding heart beats, that is to say a high heart rate with a simultaneously reduced pumping capacity on the part of the heart.
Apparatuses for detecting and treating such tachycardia phenomena, for example cardioverters or defibrillators, are well-known. A disadvantage of the known apparatuses are that they detect a tachycardia situation only when it has already occurred.
Accordingly, a need exists for an apparatus which is capable of detecting a tachycardia before the event occurs, that is to say before the beginning of the tachycardia.
The present invention is directed to a cardioelectric apparatus for early detection of a tachycardia of a heart. The cardioelectric apparatus of the current invention includes the following components:
a) measurement means for sensing the heart rate and the action potential duration, the measurement means having at least one output for the output of measurement value pairs of mutually associated measurement values for the heart rate and action potential duration;
b) measurement value processing means connected to the output of the measurement means for receiving the measurement value pairs, the measurement value processing means adapted to derive from the measurement value pairs time-variant parameters which describe the heart;
c) a memory in which comparative values characterizing a tachycardia risk are stored; and
d) an evaluation unit connected to the memory and the measurement value processing means for receiving the parameters derived from the measurement value pairs, the evaluation unit being adapted to compare the derived parameters to comparative values stored in the memory and to output a tachycardia risk signal if the comparison of the derived parameters with the comparative values shows that the derived parameters are within the tachycardia risk range.
In such an embodiment, the cardioelectric apparatus of the invention is capable of detecting a threatening tachycardia before it occurs. Any method of deriving from the measurement pair values time-variant parameters which describe the heart may be utilized in the current invention, but one method is described in detail hereinafter. Likewise, any conventional method of deriving the heart rate, that is to say the pulse rate of the heart, and the action potential duration, may be utilized. In addition, any conventional design of the apparatus such that it is in a position to establish whether certain parameters fall into a certain parameter range may be utilized in the current invention.
In an alternative embodiment, the cardioelectric apparatus of the current invention is adapted to sense at least two measurement value pairs at different measurement times. In such an embodiment, the cardioelectric apparatus additionally comprises a second storage means or memory connected to the measurement value processing means, the memory being capable of storing at least the parameters derived for the two latest measurement times, the cardioelectric apparatus further comprising trend-determining means connected to the second memory adapted to determine a trend for the future development of the parameters on the basis of the stored parameters, wherein the evaluation unit is connected to the trend-determining means and is so designed to output the tachycardia risk signal when the derived parameters are in the proximity of the tachycardia risk range and the trend for future development of the parameters points in the direction of the tachycardia risk range. In such an embodiment, the cardioelectric apparatus according to the invention is capable of detecting a tachycardia risk before the ascertained parameters fall into a dangerous range, by determining when the parameters derived from the measurement value pairs are trending toward the risk range.
In another alternative embodiment of the present invention, the cardioelectric apparatus is adapted to sense at least two measurement value pairs at different measurement times and additionally has a second storage means or memory which is connected to the measurement value processing means to store at least the parameters derived for the two respective latest measurement times. The cardioelectric apparatus further comprises trend-determining means connected to the second memory and adapted to extrapolate future parameters from the stored parameters, wherein the evaluation unit is connected to the trend-determining means and is adapted to compare the extrapolated parameters to comparative values stored in the memory and to output a tachycardia risk signal if the comparison of the extrapolated parameters with the comparative values shows that the extrapolated parameters are in the tachycardia risk range.
In yet another alternative embodiment of the present invention, the derived parameters describe time-variable bidirectional ion currents between the cell interior and the cell exterior of heart muscle cells, which include a static and a dynamic potassium ion current and a calcium ion current. In such an embodiment, the first of the parameters (xcfx84x) is a time constant of the dynamic potassium ion current, and the second of the parameters (g) is a difference (ACaxe2x88x92AKl), related to the amplitude of the dynamic potassium ion current (AKx), of the amplitudes of the calcium ion current (ACa) and the static potassium ion current (AKl) according to the equation:
g=((ACaxe2x88x92AKl)/AKx)xe2x80x83xe2x80x83(1)
In still another alternative embodiment of the present invention, the first parameter (xcfx84x) represents the time constant of the dynamic potassium channel of the heart muscle cells, and the second parameter (g) represents the ratios ((ACaxe2x88x92AKl)/(AKx)) between the permeabilities of the calcium channel (ACa), the static potassium channel (AKl), and the dynamic potassium channel (AKx) of the heart muscle cells.
In still yet another alternative embodiment of the present invention, the cardioelectric apparatus comprises an electrostimulator, such as a cardioverter, or a defibrillator, wherein the electrostimulator is connected to the evaluation unit for receiving the tachycardia risk signal and is adapted to be triggered by the tachycardia risk signal to output tachycardia-combating electrical stimulation pulses to the heart.